1. Field of the Invention
The present invention relates to a polypropylene-based composite composition. More particularly, it relates to a polypropylene-based composite composition which is directly paintable without need of treatment with a primer comprised of chlorinated polyolefins.
2. Background of the Related Art
Composites based on polypropylene have advantages such as excellent mechanical properties, processability and low production cost and thereby, have been developed into various products and applied to diverse applications. Particularly, their use is expanded to materials for interior/exterior of automobiles recently. Many parts of automobiles are made of these composites. However, they are disadvantageous in that when they are applied as an exterior material, painting and printing for surface decoration to satisfy the various requirements of consumers cannot be readily performed. Therefore, for painting a polypropylene-based composite, it is necessary to use a primer comprised of chlorinated polyolefins. The primer represented by chlorinated polyethylene or chlorinated polypropylene is a main cause of environment pollution and an increase of production cost and thus, various techniques have been developed to eliminate its use.
There has been known the molded-in-color method as a technology not needing primer treatment upon the painting of the polypropylene-based composite. This comprises mixing in a pigment during the production of the composite. It is advantageous in that it does not need an additional painting process but is disadvantageous in that it is difficult to express diverse colors and to control color and the productions cost of the composite is increased by increasing in the used amount of the pigment, dissimilarly to the painting technology.
Also, there has been developed a surface treatment technology to improve paint adhesion using flame plasma instead of primer treatment. This is aimed at providing with polarity for the surface by oxidizing the surface of a molded body of the polypropylene-based composite with high temperature flame plasma, thereby increasing adhesion strength with a paint. However, it has defects in that expensive plasma treatment equipments are additionally needed and due to characteristics of the plasma equipment, the treatment is not effectively done or overdone in an indented part and a weldline site formed upon moulding, whereby it is difficult to produce uniform paint adhesion and to thereby obtain a desired coating, dissimilarly to the primer treatment
Also, Korean patent Publication No. 1998-0060232 disclosed a method including addition of a modified resin containing a polar group (maleic anhydride grafted polypropylene, maleic anhydride grafted ethylene-propylene rubber and the like) as a technique to develop a polypropylene-based composite without need of primer treatment by using a functional additive. This technique aimed to provide polarity to the surface of a polypropylene, composite by using a modified resin with high polarity, thereby improving paintability. However, there were defects such as increase of production cost and deterioration in properties of the composite resulting from use of the expensive modified polypropylene in a large amount.
Korean Patent Publication No. 1995-0011526 disclosed a technique for improving surface polarity of a polyolefin based composite by using a polyol with a particular chemical composition having a lot of hydroxyl functionality as an additive so that the composite is directly paintable. However, the technique has defects such as increase of production cost and deterioration in properties of the composite caused by use of the expensive additive.
U.S. Pat. No. 6,133,374 disclosed a technique to improve polarity of a composite material by using a method for blending a resin modified with a functional monomer such as unsaturated carboxylic acid or acid anhydride and an epoxy resin. This patent aimed to realize direct painting by introducing an epoxy resin, since the addition of a modified resin had a limit in improvement of surface polarity of a composite. However, there were problems such as increase of production cost caused by addition of the epoxy resin and deterioration in properties caused by lack of compatibility between the epoxy resin and the polypropylene resin.